The present invention relates generally to power transmission chains and, more particularly, to power transmission chains of the roller chain variety, such as those used primarily in automotive engine timing applications. Specifically, the present invention relates to a roller chain having an improved link plate profile for improved strength. The invention can also be applied to other automotive and non-automotive applications where an improved-strength roller chain is desired.
In a power transmission application, a roller chain is wound around at least two sprockets, with the sprocket teeth engaging rollers or bushings between the links of the chain. Rotation of a driving sprocket causes power transmission through the chain and consequent rotation of at least one driven sprocket.
A typical roller chain consists of alternate inner links and outer links. The outer links, which are sometimes known as "pin links," consist of spaced link plates each having a pair of openings or apertures. Pins are tightly received in the apertures of the outer links. The inner links, which are sometimes known as "bushing links," consist of spaced link plates each having a pair of openings or apertures. Bushings are tightly received in the apertures. The bushings freely rotate about the pins, so that the inner links are pivotally connected to the outer links or able to articulate with respect to the outer links.
In some roller chain designs, cylindrical rollers surround the bushings, and when the roller chain is wrapped around a sprocket, the teeth of the sprocket received between the laterally spaced link plates and contact the longitudinally spaced rollers. These types of roller chains are sometimes called "true roller" chains. In other roller chain designs, referred to as "rollerless" chains, rollers are not deployed on the bushings, and, instead, the sprocket teeth are received between and contact the bushings themselves. Examples of roller chain are found in U.S. Pat. Nos. 4,186,617 and 5,226,856, which are both incorporated herein by reference.
During operation, the turning of the sprockets applies tension to the chain, resulting in large stresses applied to the links of the chain. In addition, the tension in the roller chain may vary as a result of considerable load variations. For example, the roller chain may be employed in an application wherein the chain undergoes sudden stoppages in chain travel, or sudden reversals in the direction of chain travel. Alternatively, the tension in the chain may vary as a result of wide variations in temperature and thermal expansion coefficients among the various parts of the engine. For these reasons, fatigue strength and ultimate strength are prime considerations in roller chain design.
One feature of roller chains that significantly impacts the strength of the chains is the manner of securing the pins and bushings into the link apertures. The most common method used involves providing for an interference fit between the pins and bushings and the corresponding link apertures. In addition to securely positioning the pin or bushing into an aperture, interference fitting or press fitting introduces dislocations into the internal structure of the metal in the vicinity of the aperture. These dislocations increase the strength and hardness of the metal in a process similar to strain hardening. The benefits associated with the processes of interference fitting depend to a certain degree on the pins and bushings sufficient strength to resist major deformation as a result of the interference fitting. An example of the use of interference fitting to increase link fatigue strength is disclosed by Jeffrey, et al., U.S. Pat. No. 3,359,815 which is incorporated herein by reference.
Aside from press fitting of the pins and bushings, another factor in roller chain design is the importance of minimizing the mass of the chain links. The impact load on the roller chain resulting from the impact of the chain links against the sprocket teeth is closely correlated to the mass of the chain. Consequently, a major problem in the design of roller chains is the task of increasing the chain strength while minimizing increases in the mass of the chain.
Various methods have been employed to increase the strength of roller chain links. For instance, the device disclosed in Lauenstein, U.S. Pat. No. 2,517,497, is directed to reinforcing the areas around the pin apertures of the link plates. In Lauenstein, the edges of the pin holes are cold coined to increase the fatigue strength of the metal along the edge of the pin aperture. However, cold coining is a costly and time consuming process and, moreover, the increase in the strength resulting from cold coining is limited.
The device disclosed in Edwards, U.S. Pat. No. 2,722,843, is also directed at increasing the strength of the link plate by reinforcing the link plate in the immediate vicinity of the pin apertures. In Edwards, the edges of the pin apertures are pressed and stamped to form tubular extensions of the link plate extending inwardly in the lateral direction. This increases the bearing area of the link plate against the pin, which prevents excessive unit bearing loads on the edges of the pin apertures. The disadvantages of this method include the difficulty and costliness of the stamping process, given the requirement that the tubular extensions must be of precise length to allow the link plates to form a tight fitting chain.
Because of the need to minimize mass of the link plate, other conventional designs have focused on adding material to the portions of the link plate where the greatest stress is applied. For instance, the device disclosed in Jeffrey, U.S. Pat. No. 3,359,815, utilizes link plates that are thicker in the vicinity of the apertures. Buttresses, which are radially symmetric about each aperture, are added surrounding the aperture. The buttresses extend in the lateral direction. Chain links of this design may be difficult to manufacture and may result in a chain that is unacceptably thick to the engine designer.
A better roller chain design is one that has increased strength in the particular areas where failure is most likely to occur without a significant increase in the thickness of the links or a major increase in link mass. Although it has been previously known that failure originates at the edge of the aperture, experimental experience and analysis indicate that, for conventional chains having pins or bushings press fit into their apertures, the maximum working stress which causes fatigue failure occurs on the aperture within an arcuate section defined by a line extending radially from the center of the aperture in a direction perpendicular to the line connecting the two aperture centers, i.e the pitch line of the link plate, and another imaginary line originating from the same center of the aperture and extending radially toward the outer surface of the end section, this second line being displaced approximately 30-45 degrees from the first perpendicular line. Accordingly, the present invention is directed to a roller chain having link plates with added material in that region. The additional material at the point where fatigue failure is likely to occur gives the link plate more resistance to fatigue failure.
However, because the material added is located on the portion of the link plate most susceptible to fatigue failure, the amount of added material is efficiently minimized, thus minimizing the mass added to the link plate. In addition, the present link plate may be produced by standard stamping or blanking, thus avoiding the problems of manufacture experienced by other link plate designs directed to increasing the strength of the link plate.
Accordingly, it is an object of the present invention to provide a roller chain with increased tensile strength, and, more particularly, increased fatigue strength. Another object of the present invention is to provide a roller chain of increased strength which can be manufactured using standard blanking methods. A further object of the present invention is to provide a roller chain having an optimized link profile with maximum material added in the areas of potential fatigue failure the amount of material added being dependent on the size sprockets the chain must wrap.